The invention pertains to increasing the performance of fuel injected engines. Although traditionally this has meant diesel engines, increasingly fuel is injected in modern gasoline engines as well.
Injectors may be of the unit injector type, in which each injector actually forces fuel into the engine cylinder, or of the simple nozzle type in which the diesel fuel pressure is generated by a central pump and then ducted to the nozzles which inject them into the cylinder. In this application, all references to "injectors" mean unit injectors, not the simple nozzle injectors.
When diesel engines are rebuilt and tuned, the injectors are either replaced, or the old injectors are cleaned, rebuilt and reinstalled in the engine. Engine performance is generally improved after a rebuilding, which is reflected in a slightly lowered fuel consumption and a corresponding increase in miles per gallon of the vehicle.
When injectors are installed in a diesel engine, either originally, or after being rebuilt, they must fall within a range of flow-rates dictated by the manufacturer. For example, a particular engine might require injectors that are rated between 54 and 60 cc's, meaning that the injector will inject that volume of fuel per 1000 strokes. Thus, any injector that fell within the six cc rating range would be adequate for the engine in question. Thus, injectors falling within the range are installed in the cylinders irrespective of the particular, relative performance of any particular cylinder or cylinders.
However, the cylinders themselves also differ considerably from one to the next in the same engine in overall performance. The difference in compression between the cylinders of an engine that is working fairly well might be 30 or 40 PSI. Although ideally each cylinder should achieve about the same compression, and produce about the same power so that the power output is even throughout the entire engine cycle, diesel engines are tuned more or less roughly, with these substantial variations between cylinders being acceptable. No effort is made to match the injectors, for example, with the cylinders so that the performance of the particular injector compliments the performance of a particular cylinder so that together the cylinders all perform at about the same rate, resulting in smoother engine performance and greater mileage.
Electronically controlled injector systems control all of the injectors simultaneously based on various input data, and the central controller, or "electronic control module" (ECM) controls all of the injectors together to maximize efficiency, or power, or otherwise utilize the data to optimize engine performance.
Electronic control systems do not, however, control the fuel injected to each individual cylinder based on the temperature or pressure sensed in that cylinder. The electronic control system would thus work ideally if all of the cylinders operated at substantially identical temperatures and pressures, which of course, they were designed to do. However, in actual practice and especially over a period of time resulting in engine wear, this ideal situation by no means exists.